A radiation imaging device is one of the devices which use radioactive isotope to obtain an image and which is being widely used in the field of a nondestructive testing as well as a nuclear medicine diagnosis.
A radiation imaging device used in the field of nuclear medicine diagnosis, i.e., a gamma camera using gamma rays or a single photon emission computed tomography (SPECT) device, provides a human's functional information by using radiopharmaceutical, differently from other diagnosis devices, i.e., a magnetic resonance imaging (MRI) or a ultrasonic diagnostic device, which provide a human's structural information.
FIG. 1 represents a construction of a general gamma camera 1. The general gamma camera 1 comprises a collimator 10, a crystal scintillator, i.e., a scintillator 30 and a photomultiplier tube (PMT) 50.
The collimator 10 acts as a collimator which allows gamma rays discharged from a chaser in a body and having the same direction as the camera to pass through and blocks gamma rays having different direction. That is, the collimator 10 geometrically limits gamma rays released from a body part so that only gamma rays released from a required part enter into the scintillator 30.
Here, gamma rays which pass through the collimator 10 and reach the scintillator 30 is transformed into an electromagnetic wave having low energy, i.e., visible rays, which can be easily detected by the scintillator 30. Then, the rays are amplified in the photomultiplier tube 50 and are transformed into electric signals and the detected position or energy is stored on a computer 70 so that the image can be obtained.
Such a gamma camera is disclosed in Korean Patent No. 0841123.
A single photon emission computed tomography (SPECT) device is firstly invented by W. I. Keys in 1976 and the device for brain is developed by R. J. Jaszczak in 1979.
A single photon emission computed tomography (SPECT) device has similar operation to the gamma camera 1. It is configured such that a single photon, i.e., gamma ray, which releases radioparmaceutical is inserted into a body and a scintillation camera installed on a head rotating around the body detects at various angles that the gamma ray generated in the body penetrates the body, and tomographic cross-section images are obtained from detected signals by means of an image reconfiguration algorithm.
Therefore, like the gamma camera 1, the single photon emission computed tomography (SPECT) device also comprises a collimator 10, a scintillator 30 and a photomultiplier tube (PMT) 50.
As described above, a gamma camera 1 or a single photon emission computed tomography (SPECT) device uses a collimator through which gamma rays pass selectively and the collimator is generally made of lead or tungsten and has a fixed shape.
FIGS. 2A and 2B show a pin-hole collimator 10 of prior arts which is used in the gamma camera 1 or a single photon emission computed tomography (SPECT) device.
The pin-hole collimator 10 comprises a main body 11 constituting the entire structure and a pin-hole 12 through which gamma rays pass. As shown in FIG. 2, the pin-hole 12 is divided into the first cone region 13, a penetrating hole region 15 and the second cone region 14.
FIG. 3 shows a multiple pin-hole collimator 10a of prior arts. As shown in FIG. 3, a main body 11a has a plurality of pin-holes 12a and the plurality of pin-holes 12a are arranged vertically (see FIG. 2B) or inclined (see FIG. 7A).
Here, the shape of the pin-hole 12a is defined by the radiation angle of the first cone region 13 and the second cone region 14, the diameter and the length of the penetrating-hole region 15, etc. and the shape is determined by the size or location of the object to be taken, the size or location of the scintillator 30 and the energy of gamma rays.
But, since the shape of the pin-hole collimator 10 of prior arts is fixed as shown in FIGS. 2A, 2B, and 3, if the imaging condition such as the size or location of the object is changed, the pin-hole collimator 10 must be replaced with other collimator corresponding to the changed condition, thereby causing inconvenience.